Suppress unchanged organization branding events

[aldoborrero]

Summary

• Suppress org_branding_updated when all branding fields are unchanged, as required by the plugin event contract.
• Lock the organization's latest branding row and use a conditional update, so concurrent saves report only actual changes and unchanged saves preserve the row version.
• Keep manager authorization and post-commit dispatch intact; return a not-found error for a missing organization.
• Regenerate the SQLx query cache. No schema or dependency changes.

Validation

• Five SQLx regressions exercise the production mutation helper: unchanged saves, all 12 fields with null/empty transitions, concurrent repeat/restoration, and missing organizations.
• The unchanged-write regressions fail against the original unconditional write and pass with the fix. Tests verify the change flag consumed by dispatch, not end-to-end WASM event delivery.
• Full core and server suites: 531 passed, 5 existing ignored tests.
• Server/all-targets Clippy with warnings denied; Rust formatting and diff checks passed.
• WASM compilation passed with the same three existing warnings (InvoiceLine, OrgBranding, PluginWidget).
• Tests and query preparation use an isolated, migrated PostgreSQL instance, not the development database.